Thin-film devices are devices which are constituted of a plurality of stacked layers which together constitute an electrical circuit, an electro-optical element or an optical element. Such electrical circuits typically are miniaturized electrical circuits, also known as Integrated Circuits or in short ICs, comprise stacks of conductive, semi-conductive and insulating layers. The electro-optical elements comprise stacks which, for example, constitute a light emitting diode, an organic light emitting diode or a laser diode, and thus typically at least partially have an electrical circuit equivalent to a diode-circuit combined with a light emitting layer which may, for example, be constituted of an organic light emitting layer which results in an Organic Light Emitting Diode (further also referred to as OLED). Optical elements may comprise of several optical layers constituting an optical circuit comprising, for example, light guides and light gates. Such optical elements often may be designed to perform similar functions as Integrated circuits and are often designed to replace Integrated circuits.
All of these thin-film devices require some kind of sealing to protect the devices from environmental influences. The quality of the seal provided to the thin-film device often determines the operational life-time of the thin-film device. Especially when the thin-film device is an OLED device, the sealing of the OLED device is crucial because water causing corrosion effects inside the OLED device often locally generates black spots in the OLED device. Black spots due to the corrosion effect continue to grow radially starting from, for example, a local breach in the sealing layer. Over time, the corrosion effect becomes visible to the human eye which typically is unacceptable when the OLED device is used for illumination purposes. Eventually the corrosion effect may destroy the whole OLED device preventing the OLED device from producing any light.
In known thin-film devices, the sealing may be done via a sealing chamber in which the thin-film device is located. However, to reduce a thickness of the thin-film device and to also reduce production cost of the thin-film device, the sealing is preferably done via a sealing layer directly applied to the thin-film device. Such sealing layers are well known, especially applied to OLED devices. Known sealing layers may, for example, comprise a stack of a plurality of layers comprising silicon nitride-organic material-silicon nitride. The organic layer may be relatively thin (few 100 nm), providing an effective decoupling of pinholes in the surrounding nitride layers. Alternatively, the organic layer may be relatively thick and thus also planarize particles which may be present in any of the layers. Such stack of layers constituting the sealing layer does not prevent black-spots from occurring, but delays the growth of the black-spot as it forms a labyrinth for the water to enter the OLED device.
Alternatively the sealing layer may be constituted of a plurality of inorganic layers or a layer constituted via electrochemical plating. The inorganic layers, for example, comprise stacks comprising silicon nitride-silicon oxide-silicon nitride, or silicon nitride-silicon oxinitride-silicon nitride, further also referred to as NON-stacks. Such NON-stacks typically comprise several repetitions of this basic stack, for example about eight layers (i.e. NONONON in which N represents silicon nitride and O represents silicon oxide). In these alternative sealing layers, the number of black spots occurring is strongly reduced. However, any remaining local breach in such alternative sealing layer causes the black-spot to continuously grow relatively fast (becoming visible within approximately 1 hour in a dampish environment). The occurrence of such a local breach is a production yield problem (# local breaches per surface area), which is disadvantageous for smaller devices, but is a much more serious problem for the production of larger devices.
So a disadvantage of the known sealed thin-film devices is that the operational life-time of the thin-film device is still too limited.